A mechanical tangential striking mechanism such as the one used in a handheld power tool of the above-mentioned type, for instance, in an impact screwdriver, allows the generation of relatively large torques on the tool socket, whereby only a relatively small counter-torque is needed. This is advantageous, for example, when screwed connections are being tightened or when screw anchors are being set into a very hard substrate. In particular, it is an option in such applications for the peak torque that can be provided by the tangential striking mechanism to be far higher than the continuous torque that can be provided by the drive of the handheld power tool. The lowest possible counter-torque is especially advantageous for users since they normally have to exert the counter-torque onto the handle of the handheld power tool such as, for example, an impact screwdriver. The lower the counter-torque, the simpler the handling of the handheld power tool.
For the most part, tangential striking mechanisms within the scope of a spring-mass system are designed for the resonant operation of such a system, which usually restricts the effective operation to a relatively limited torque range. Ultimately, the actual operating point of the handheld power tool within the relatively narrowly limited torque range is defined by the rotational speed of the drive of the handheld power tool.
Before the above-mentioned backdrop, it is desirable to achieve the largest possible torque range within which the handheld power tool can be effectively operated. It has been found that, for this purpose, a tangential striking mechanism of the handheld power tool—similar to a spring-mass system—can be adapted for resonant operation. For instance, German patent DE 198 21 554 B4 discloses a handheld power tool with a cam striking mechanism in which a cam disk arranged non-rotatably in the housing of the handheld power tool can be axially moved against the force of a first spring, and if necessary, also against the force of a second spring that can be coupled on. This makes it fundamentally possible to increase the striking strength of the cam striking mechanism.
A problematic aspect of the adaptation of a tangential striking mechanism—which can be basically structured as a spring-mass system like the friction clutch of European application EP 1 862 265 A2—is that any change in the spring force for the mass of the hammer in the tangential striking mechanism also leads to a change in the striking frequency, which is perceptible to the user. If an impact screwdriver is being used, this naturally also influences the tightening of screws or the setting of anchors. Moreover, an increase in the spring force, for example, not only causes an increase in the striking force, but also causes the tangential striking mechanism to have a higher triggering torque, which means that the user has to apply a corresponding counter-torque onto the handle. This has a detrimental effect on the handling of the handheld power tool. In particular, a relatively low holding torque is especially desirable since this is an essential benefit of an impact screwdriver with a tangential striking mechanism in comparison to, for instance, a conventional screwdriver. In the case of the striking mechanism adaptations known so far, it has also proven to be necessary to regularly adapt the rotational speed of the motor to the adapted conditions of the striking mechanism in order to attain an effective operating point within the useful and adapted torque range.